This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
The present disclosure relates to wireline riser tensioner systems like those used in drilling operations.
A wireline riser tensioner system is designed to provide and maintain the necessary axial tension on a marine riser string as the offshore drilling vessel or rig moves vertically and laterally relative to the wellhead. The system typically includes single or dual tensioner cylinders or units arranged about a wellhead, with the tensioner units connected by way of a wire rope or cable to a tension ring (see FIG. 1). A wire rope or cable is reeved across the tensioner sheaves to provide a desired cylinder stroke-to-vessel heave ratio (e.g., one-fourth of the vessel heave). The cable is routed from the tension ring through an idler sheave, across the respective tensioner, and terminated in an anchor after three safety turns.
Pneumatically, two tensioner cylinders located opposite of each other across the well work together as a pair. The tensioner cylinders have a fluid side and a gas side. The fluid side is between a cylinder piston and a floating piston in a high pressure accumulator. The gas side is on the opposite side of the floating piston in the high pressure accumulator. This arrangement allows the tensioner system to work as a set of large hydraulic-pneumatic springs across the well center.
Using this setup, the tensioners cannot serve a second wellhead unless the tensioners are moved, skidded, or slid into a different location, or unless the tensioners include “direct-acting” cylinders. However, direct-acting cylinders present challenges of their own, and the majority of wireline riser tensioners in new drilling rigs are traditional ones.